The present invention relates to a color management method and apparatus for a printing press, which measure the colorimetic values of each profile generation patch printed by the printing press and generate a profile representing a color reproduction characteristic of the printing press from the measured colorimetic values of each patch and the dot area percent of each ink color predetermined in correspondence with each patch and, more particularly, to a color management method and apparatus for a printing press, having a function of checking the stability of the printing press.
Generally, when printing products are ordered, a color proofing print is presented to the customer in advance to confirm the tint of final printing products. More specifically, a color proofing print output from a color proofing apparatus (flat-bed proofing machine, color printer, DDCP (Direct Digital Color Proofer), or simplified proofing machine) is presented to the customer to confirm whether the tint is appropriate. If the customer agrees to the tint of the color proofing print, the ink supply amount of each ink color in a printing press is adjusted so that actual printing products are set to have the same tint as that of the color proofing print.
However, it is very difficult to obtain printing products with the same tint as that of the color proofing print by adjusting the ink supply amount of each ink color in the printing press because the color proofing apparatus and printing press have different color reproduction characteristics. Thus, the printing company has troubles with the customer in some cases.
To solve this, recently, the color reproduction characteristics of the color proofing apparatus and printing press are checked in advance, and color proofing is done by tint according to the tint of printing products printed by the printing press, thereby preventing troubles with the customer. More specifically, a profile representing the color reproduction characteristic of the color proofing apparatus is compared with a profile representing the color reproduction characteristic of the printing press, and, according to the comparison result, the dot area percent of each ink color in outputting a color proofing print, i.e., for a four color printing, the dot area percent (printed area of a color per unit area) of each of ink colors, including yellow, magenta (red), and cyan (blue), and black is adjusted such that the color proofing print and printing products printed by the printing press have the same tint. This processing of adjusting to have the same tint by the apparatus and printing press is called color matching.
The profile of an existing printing press provided by press makers has large error because a printing company employs various output conditions and printing conditions (e.g., output and printing environments, printing materials, inks, paper, reference density values, and client requirements). For this reason, the profile of a printing press is individually generated using a measurement device under the output and printing conditions in the printing company.
FIG. 9 shows a profile generation printing product printed by a printing press (not shown). A profile generation color chart 5-1 is printed at the center of a printing product 5. For a general four-color printing product using black, cyan, magenta, and yellow inks, the profile generation color chart 5-1 is formed from a number of patches 5a having different values in the dot area percent of the respective ink colors, e.g., black 5%, cyan 10%, magenta 10%, and yellow 10%, or black 5%, cyan 20%, magenta 10%, and yellow 20%. The colorimetic values of each patch 5a of the profile generation color chart 5-1 are measured, and the measured colorimetic values of each patch 5a are made to correspond to the dot area percent of each ink color predetermined in correspondence with each patch 5a, thus serving these relationships as the printing press profile.
In a case in which colors are managed using a profile, color matching precision depends on the stabilities of printing press and color proofing apparatus. Since the stabilities of the printing press and color proofing apparatus change in accordance with a change in environment or aging (e.g., the exhaustion of a blanket), the stabilities must be adjusted every time they change. The general color proofing apparatus is easily readjusted by an additional function called calibration, but the printing press does not have such a function. Thus, daily maintenance for the printing press is very important.
Even if the maintenance has been frequently done, the operator does not know when the stability of the printing press changes. When the operator does not find a change in stability of the printing press, the printing product printed by the printing press and the color proofing print output from the color proofing apparatus have the different tints until the next maintenance is done. When finding a change in stability of the printing press, the operator must adjust an ink supply amount manually to maintain color matching precision until the next maintenance is done. This operation is very time-consuming and imposes a severe burden on the operator.
It is an object of the present invention to provide a color management method and apparatus for a printing press, which can find a change in stability of the printing press early.
It is another object of the present invention to provide a color management method and apparatus for a printing press, which can easily maintain color matching precision within a short time even when the stability of the printing press changes.
In order to achieve the above objects, according to the present invention, there is provided a color management method for a printing press, comprising the steps of measuring colorimetic values of a first patch for generating a profile printed by the printing press to generate a printing press profile representing a color reproduction characteristic of the printing press from the measured colorimetic values of the first patch and a dot area percent of each ink color predetermined in correspondence with the first patch, measuring colorimetic values of a second patch for determining stability of the printing press printed by the printing press, comparing the measured colorimetic values of the second patch with colorimetic values, in the printing press profile, having a dot area percent substantially equal to a dot area percent of each ink color predetermined in correspondence with the second patch, and generating a warning on the basis of a comparison result.